This invention pertains to a distance-measuring system suitable for use with devices such as cameras, proximity detectors, and the like.
Such devices usually have a range of focus or range of operation within which presence of an object will be registered and outside which an object will not be detected. In applications such as proximity detectors which are designed to inform a user whether or not an intruder enters a protected zone, it would be advantageous to provide a distance-measuring system which would inform a user whenever such a zone was entered.
Moreover, since systems of this type may be used with a camera or other device which tracks distance within the zone precisely, it would be advantageous to provide a system of this type which informs a user whenever an object is located within a range of focus, while still permitting connection of ancillary switching circuitry which can be used to allow the camera to be automatically focussed.
Furthermore, it would be advantageous to provide a system of this type which would operate in such a fashion that the effects of high frequency noise would be eliminated, whereby false triggering of the system caused by noise would be eliminated.